This research program is designed: 1) to study the development of the sensory epithelia of the inner ear and the cytodifferentiation of the sensory cells at the three phases of embryonic development in organ culture and in vivo, and 2) to determine the factors influencing histogenesis and cytodifferentiation of the sensory epithelia. The embryonic chick inner ear is being used as a model for these studies. The methods of organ culture, histologic procedures, differential staining, and electron microscopy are being used in these studies. 1. Phase I. This is the proliferative phase in which presumptive sensory epithelia become localized. Phase 2 is the mid-point in development. Morphologic formations of the cristae and basilar papillae are established and a few hair cells can be demonstrated in histologic preparations and electron micrographs. Phase 3. Completely formed sensory structures have developed in culture and in vivo; sensory epithelia have differentiated into hair cells and supporting cells. 2. Experiments are designed to determine: a) the requirement for mesenchyme for histogenesis of the sensory epithelia, and b) the influence of innervation of the sensory epithelia on cytodifferentiation of the sensory cells. BIBLIOGRAPHIC REFERENCE: Orr, M.F. The influence of mesenchyme on the development of the embryonic chick otocyst epithelium. J. Cell Biol. 70, 155a, 1976.